Porous structures design in liquid silicone rubber foams through CO2 controlled molecular crosslinking

During CO2 foaming, molecular crosslinking plays an important role on cell structure of rubber foam. In this work, effects of CO2 on crosslinking reaction of liquid silicone rubber (LSR) were investigated according to viscoelasticity and reaction activation energy. It was found that CO2 facilitates formation of local primary crosslinking structure in LSR, while inhibiting creation of crosslinking network. When saturation pressure was lower than 13 MPa, LSR foam can obtain uniform cells only under a narrow saturation time. After increasing CO2 pressure higher than 13 MPa, cell structure was less affected by saturation time and time window for preparing uniform cell structure was extended. LSR foam was prepared with minimum cell size of 22.1 μm as well as maximum expansion ratio of 4.9. This work demonstrates CO2 controlled molecular crosslinking is key to porous design of LSR, which exhibits good theoretical exploration and application value in preparation of LSR foam.